The present invention relates to a semiconductor integrated circuit and a drive apparatus including the semiconductor integrated circuit. More particularly, the invention relates to a semiconductor integrated circuit that transmits signals via an isolation element, and to a drive apparatus that includes the semiconductor integrated circuit.
Isolation elements such as the photo-coupler, inductor-coupled isolator, capacitor-coupled isolator, and GMR (Giant Magneto Resistive) element isolator are currently used as the means for transmitting signals between a plurality of semiconductor chips each operating on a different source voltage.
For example, the photo-coupler uses one chip to convert an electric signal to an optical signal before getting another chip to convert that optical signal to an electric signal, thus providing isolation between two semiconductor chips. The inductor-coupled isolator uses one coil to convert an electric signal to magnetism before getting another coil to convert the magnetism to an electric signal, thus ensuring isolation between two semiconductor chips. The capacitor-coupled isolator uses one electrode of a capacitative element to convert an electric signal to an electric field before utilizing the other electrode of the element to convert the electric field to an electric signal, thereby providing isolation between two semiconductor chips. The GMR element isolator uses a coil to convert an electric signal to magnetism before utilizing a GMR element to convert the magnetism to an electric signal, thereby offering isolation between two semiconductor chips.
The above-described isolation elements are used in today's power control circuits such as inverter equipment and converter equipment. Specifically, this type of power control circuit of recent years operating on one power supply system transmits a control signal output from a microcomputer to a chip of another power supply system via an isolation element, thereby converting the voltage level of the control signal in question. The power control circuit proceeds to get a gate driver amplifying the control signal with its voltage level converted, before feeding the amplified control signal to a control terminal of a power transistor (output transistor) that controls currents flowing through a load.
Some related art is disclosed in the following literature: Japanese Unexamined Patent Publication No. 2009-49035 (called the Patent Literature 1 hereunder), Japanese Unexamined Patent Publication No. Hei 9 (1997)-312555 (Patent Literature 2), Japanese Unexamined Patent Publication No. 2002-84173 (Patent Literature 3), Japanese Unexamined Patent Publication No. 2004-222367 (Patent Literature 4), and Japanese Unexamined Patent Publication No. Hei 5 (1993)-29914 (Patent Literature 5).
Disclosed in the Patent Literature 1, an intelligent power module for a step up/down converter includes a CPU, an isolation transformer, a safeguard-equipped gate driver IC, and an IGBI (Insulated Gate Bipolar Transistor). The CPU generates a gate drive PWM signal designating conduction or non-conduction of the IGBT, and transmits the signal insulatingly to the safeguard-equipped gate driver via the isolation transformer. Based on the gate drive PWM signal, the safeguard-equipped gate driver IC generates a gate signal and feeds it to the control terminal of the IGBT for a switching operation. The chip on which the IGBT is formed has a temperature sensor and a current sensor.
Upon determining that the current flowing through the IGBT has exceeded a threshold value possibly triggering IGBT destruction based on an overheat detection signal from the temperature sensor and/or on an overcurrent detection signal from the current sensor, the safeguard-equipped gate driver IC transmits an alarm signal to the CPU. On receiving the alarm signal from the safeguard-equipped gate driver IC, the CPU stops generating the gate drive PWM signal and thereby cuts off the current flowing through the IGBT.
A switching circuit control apparatus disclosed in the Patent Literature 2 includes a mask circuit that masks information signals such as a temperature signal and a current signal only while switching noise is being generated from a switching circuit that repeats on and off operations. The switching circuit control apparatus detects such information signals from inside the switching circuit or from within electric circuits adjacent to and affected by the switching circuit generating the switching noise. If the switching circuit control apparatus detects an abnormality in temperature or in other parameters based on the information signals except during the masking period, the apparatus supplies a gage circuit with a gate control signal such as a switching stop command or a switching reduction command.
Consequently, the switching circuit control circuit can detect the information signals at high speed without making false determination by averting the adverse effects of the noise from the switching circuit, according to the Patent Literature 2.
The Patent Literature 3 discloses a power semiconductor device that securely protects power transistors against an overcurrent state by unfailingly detecting the generation of that state without making false determination even if noise is detected in a sense voltage obtained by having a sense current detected with a sense resistor.
A gate drive apparatus disclosed in the Patent Literature 4 drives a main semiconductor device of a power converter by the gate. The gate drive apparatus includes a voltage detection part, a waveform control circuit, a reference power source, and a voltage comparator. The voltage detection part is coupled to the collector terminal of the main semiconductor device and detects a collector voltage of that device. The waveform control circuit is coupled in electrical parallel to the voltage detection part and controls differentially the collector voltage detected by the voltage detection part. The reference power source generates a reference voltage. The voltage comparator compares the reference voltage from the reference power source with the collector voltage controlled by the waveform control circuit. Based on the result of the comparison, the voltage comparator outputs an abnormality detection signal.
In this manner, the gate drive apparatus protects the main semiconductor device from a short circuit or an overcurrent at high speed, according to the Patent Literature 4.
An output buffer circuit disclosed in the Patent Literature 5 includes an output buffer, a power source noise detection circuit, and a ground noise detection circuit. The output buffer has a first and a second PMOS transistor coupled in parallel between a power terminal and an output terminal OUT and a first and a second NMOS transistor coupled in parallel between a ground terminal and the output terminal OUT.
When the potential of the power terminal drops due to a change in the potential level of an output signal OUT, the power source noise detection circuit detects the potential drop and acts to cut off the second PMOS transistor during the potential drop period. When the potential of the ground terminal rises because of a change in the potential level of the output signal OUT, the ground noise detection circuit detects the potential rise and acts to cut off the second NMOS transistor during the potential rise period.
Thus by reducing its drive capability only during the period where the power source potential or ground potential is being changed, the output buffer circuit prevents the other circuits on the same chip from malfunctioning, according to the Patent Literature 5.